On some occasions, the adults threw parties and played card games to decide who would abuse which child, Mrs Rafferty said.

In interviews the victims described how they were abused in front of one another and other adults.

They said the abuse became so routine the victims came to accept it as normal.

The children were preyed upon during a period beginning around 15 years ago. Several victims described Black and Jason Adams taking photos and laughing.

One male victim said: ‘There would be parties and they would do some games where the boys were in one room with the men and the girls were in another with the women.

‘The adults would have a card game and the winner would get to choose a boy to start touching their private parts and then hurt them afterwards.’

Describing Black, Mrs Rafferty said: ‘Was she a helpless victim of abusive males or was she herself deeply involved with the children’s ill treatment?

‘Many of the defendants have become good at appearing normal and respectable.

‘This is what you would have to do in order to be child abusers to the extent alleged here.’

All of the defendants denied abusing the children, and claimed it simply did not happen.

During the trial it emerged that police had launched an investigation in to the conduct of Norfolk County Council social workers involved in the case.

The court heard that the trial had originally been due to start last year only to be delayed when prosecutors raised concerns over changes made by social workers to statements taken from the children.

This resulted in Norfolk Police launching an investigation into alleged misconduct.

Sarah Elliott QC, representing Black, told the court that at the time the county’s children’s services department had recently failed an Ofsted inspection, being ranked ‘inadequate’ in all areas.

The guilty defendants will be sentenced this afternoon.

Speaking outside the court, Detective Chief Inspector Pete Hornby praised the bravery of the victims and said he was satisfied with the result of a 28-month investigation.

He added: ‘This case provides a sickening glimpse into sexual abuse on a large scale.’

He said the force had concluded its investigation into the allegations made against social workers and no criminal charges would be brought.

Mr Hornby added: ‘In their tender years, these children were subjected to sexual abuse beyond most people’s imagination by adults they believed were telling the truth.

‘It is the most harrowing case I have dealt with in 23 years of policing.

‘Marie Black has been found to be at the centre of this abuse and incited others to commit abuse against them. She thought they would never speak out.

‘Today’s verdict is testament to the children’s bravery and to the hard work of dedicated professionals from a range of agencies in this case.

‘It has brought them the knowledge they are believed and, I hope, will encourage other victims of abuse to find their voice and come forward.’

Sheila Lock, interim executive director of Norfolk children’s services, said: ‘Sexual abuse against children is an horrific crime and still often goes under-reported or unnoticed.

‘The victims in this case have shown tremendous courage in speaking out and I hope that this verdict will give other victims or witnesses the confidence to report abuse – because agencies in Norfolk will listen and act.

‘This was a complex case brought by the Crown Prosecution Service, with our staff among several witnesses who gave evidence in the proceedings.

‘The needs of the children, who were central to the prosecution case, have always been at the fore of our minds and have been the main focus of all of the agencies involved.’

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